Doctors across California and in two other Western states are owed millions of dollars in backlogged Medicare reimbursements, leading some physicians to turn away elderly patients and pushing others to the brink of bankruptcy. In the most extreme cases, doctors have not been paid since February. Others are owed hundreds of thousands of dollars. Doctors who serve high numbers of Medicare patients say they are defaulting on rent, laying off staff, and begging drug suppliers not to stop shipments.